Magnet and holder assemblies for magnetron tubes



Oct. 25, 1960 M. ESTERSON ,0

MAGNET AND HOLDER ASSEMBLIES FOR MAGNETRON TUBES Filed March 11, 1957 INVENT R? g g g 404 41 United States Patent MAGNET AND HOLDER ASSEMBLIES FOR MAGNETRON TUBES Maurice Esterson, Chelmsford, England, assignor to English Electric Valve Company, London, England, a company of Great Britain Filcd'Mar. 11, 1957, Ser. No. 645,078

.fClaims priority, application Great Britain July 25, 1956 V 4 Claims. (Cl. SIS-39.71)

of the tube into the vacuum. This construction enables the magnetic air gap to be made very short and hence enables a required magnetic field to be obtained by means of a permanent magnet which is a good deal smaller and lighter than would otherwise be possible. It is also well known to be of substantial advantage in microwave multi-cavity magnetron tubes to adopt the so-called axial cathode type of construction, i.e. the type of construction in which the cathode support is axial with respect to the anode system. This type of construction has the advantage of being very robust and enables amore precisely designed and manufactured cathode assembly to be used gives better thermal dissipation than is possible with a comparable radial cathode type of construction.

Hitherto, so far as I am aware, the only magnetic vjho lder and tube arrangement which enables the advanof both the built-in pole piece type of construction' and the axial cathode type of construction to be simultaneously obtained, is the so-called and well known packaged arrangement in which the magnetic'holder,

the output wave guide, and the tube form a structurally "integrated assembly. With this known packaged arrangement, however, there is the disadvantage that, in pracgtice, a magnetic holder with the tube assembled therein, must be supplied as a complete unit. This is a practical necessity because, with the known packaged arrangement,

fitting the tube into the magnetic holder requires the use of special jigs" or fixtures, or, alternatively, the use of means for magnetizing the magnet after the tube has been assembled into the magnetic holder, so that, in practice, fitting a tube into a magnetic holder, or replacing a tube already so, fitted by another, is a factory operation. This is because the great magnetic force of the magnet, and the need for precise positioning of the tube in the'mag- I jneticholder are such that the fitting of a tube or its withthan is the case in a magnetron tube with a so-calledradial cathode mounting. Also this type of construction .drawal and replacement by another, cannot be done by hand without special equipment.

I The present invention seeks to overcome the above limitation and to provide a magnetic holder for a magnetron tube of the type referred to which shall be such that a tube can be removed and replaced without difli- 2,958,005, Patented Qct. 25, 1960 culty by hand. The achievement of this object is of great practical and commercial advantage for it means that magnetron tubes can be supplied by themselves and fitted by the user into holders in accordance with this invention. 7

According to this invention a magnetic holder for a magnetron tube of the type having an axial cathode support and so-called built-in pole pieces forming part of the evacuated envelope and projecting into the evacuated space comprises a permanent magnet having poles each of which has a face which is recessed to receive and fit the external surface of the pole piece of an inserted magnetron tube whereby, when the said tube is inserted and in use it is firmly magnetically held in a pre-determined position in relation to the magnet with its pole pieces partly embraced by the recesses in the magnet poles.

The great advantage of the invention is that it provides a magnetic holder into which 'a tube can be readily inserted and from which a tube can readily be removed by merely magnetically shorting the magnet poles to one another. Removal of a tube can thus be eflected by providing a ferro-rnagnetic keeper to bridge across the magnet poles adjacent and inwardly of an inserted tube so that the field path through the tube is magnetically short circuited to an extent sufficient to allow the tube to be readily removed and a replacement readily inserted, afiter which the keeper can be withdrawn from the poles.

Preferably the magnetic holder also includes a waveguide positioned to receive the normally provided output probe branch of the tube. If desired screw or other adjustment means may be provided to allow of adjustment of the position of the waveguide with relation to the magnet pole pieces so that, after a tube has been inserted, the degree of penetration of the output probe branch into the waveguide may be finely adjusted.

Preferably the recesses in the magnet pole pieces are arcuate to fit the surfaces of the pole pieces of a tube having externally cylindrical pole piece surfaces. This form of constructioncircular recesses and cylindrical tube pole pieces-is at present considered the best and most convenient. V

-The' magnetic holder is preferably provided with nonferromagnetic guide means leading smoothly into the recesses. I q

Preferably also the magnetic holder assembly includes a ferro-magnetic keeper and means for forcing it away from or permitting it to adopt a magnetically short-circuiting position with respect to the permanent magnet of the holder. Said keeper and means may conveniently be in the form of a ferromagnetic bar adapted to bridge the magnet poles and having threaded holes through which pass bolts having ends adapted to enter suitably positioned blind holes in the magnet poles.

The invention is illustrated and explained in connection. with the accompanying drawings in which:

Fig. 1 is provided for purposes of explanation and is a sectional elevation of -a typical known magnetron tube of the type referred to; and

Figs. 2,3 and 4 are mutually perpendicular views of a preferred form of magneticholder in'accordance with the invention, Fig. 2 showing in broken lines a magnetron tube of the type illustrated in Fig. 1 in position in the magnetic holder.

.There are two built in pole pieces P1 and P2,'the coaxial cathode structure passing centrally through the pole piece P1. The pole pieces P1 and P2 form part of the evacuated envelope of the tube and, as will be seen, they terminate closely adjacent the anode system A on either side thereof. Output is taken by means of an output probe OP in a branch B of the tube. The

What I claim as new and desire 'to secure by Letters Patent of the United States is: pole pieces P1 and P2 are circular in section and have cylindrical external faces F1 and F2.

The preferred form of magnetic holder in accordance with this invention and shown in Figs. 2, 3 and 4, comprises a powerful permanent magnet 1 of more or less U-form with two poles 2 and 3 extending parallel to one another and spaced apart by the distance between the cylindrical surfaces F1 and P2 of the tube for which the holder is designed. The end of each pole 2 and 3 is provided with an approximately semi-circular recess 4 shaped to correspond with and to fit the external cylindrical surfaces F1 and F2. The magnet 1 is mounted on a base plate 5 to which it is held by means of a screw (not shown) which passes through the base plate into the magnet. Preferably the screw passes through a slot (not shown) in the base plate to enable the magnet to be locked in any position within a range of adjustment provided by the direction of the length of the slot, so as to enable the magnet to be adjusted (to right or left in Fig. 4) with reference to the base plate 5. Also mounted on the base plate 5 is a length of rectangular waveguide 6 which is closed at the top (the top in Fig. 4, that is) and which is open at the bottom. This waveguide length has a transverse tube 7 entering it at right angles and adapted to receive the normally provided output probe branch B (Fig. 1) of a tube which the magnetic holder is designed to receive. In Fig. 4, 8 represents the usual adjusting screw for adjustment of the waveguide.

Non-magnetic guide means 9 (best shown in Fig. 4) and attached to the magnet 1, provide a guide surface 9 which is in effect a continuation of the bottom edges of the recesses 4 so that when a tube is placed with its pole piece surfaces F1 and F2 on the surfaces 9 it will be in position to have its pole piece surfaces F1 and F2 easily entered into recesses 4.

Across the poles 2 and 3 and bridging them inwardly of the recesses 4 is a ferro-magnetic keeper bar 10 having two tapped holes through which pass threaded bolts 11 which screw into the said holes and which have the vthreads turned off at their far ends. These far ends enter into blind hola 12 (best shown in Fig. 3) in the pole pieces. When the bar 10 is in the position shown in Figs. 2, 3 and 4 it provides a magnetic short circuit between the poles 2 and 3 so that the magnetic force by which an inserted tube (as shown in dotted lines in Fig. 2) having its pole surfaces F1 and F2 in the recesses 4, will be held by the magnet, will be very much reduced. The tube can therefore be withdrawn without much difficulty with the fingers. Thus a tube can be removed and replaced by hand, the replacement tube being led easily into its correct position over the guide surfaces 9*. The bolts 11 serve as a means for locating the keeper 10 in a selected one of any of a plurality of short circuiting positions with respect to the permanent magnet 1. When a new tube is in position the bolts 11 are screwed down through the tapped holes in the keeper bar and accordingly force the said :bar away from the pole pieces 2 and 3 thus removing the magnetic short circuit. In practice, if the bar 10 be forced up until it is about /2" or /1" above the pole pieces 2 and 3 its effect as a magnetic short circuit will be quite small and an inserted tube will be operable and firmly held in its correct position with its output probe branch projecting through the tube 7. Indeed a small measure of adjustment of the magnetic field through an inserted tube is obtainable by adjusting the level of the bar 10 with respect to the poles 2 and 3. The principal object of the blind holes 12 in the poles 2 and 3 is to ensure that when the bolts are screwed down to force up the bar 10 the said bar will not tilt over towards the poles from which it is being forced.

The screw and slot arrangement (not shown) for enabling the magnet to be adjusted sideways (in Fig. 4) with reference to the waveguide 6 provides a convenient means of ensuring correct penetration of the output probe of a tube into the waveguide when one tube is replaced by another.

It will be seen that, with this arrangement, it is a comparatively simple matter to replace one tube by another by lowering the bar 10 until it contacts with the poles 2 and 3; pulling out the magnetron tube against the remaining magnetic attraction; inserting a replacement tube (there will be enough remaining magnetic force to ensure that the replacement tube is drawn with its pole piece surfaces F1 and F2 firmly against the recesses 4, but not so much force as to present any difiiculty in correctly inserting the new tube); and then screwing down the bolts 11 to force the bar oh the magnet poles.

I claim:

1. In combination, a magnetic holder and magnetron tube comprising a magnetron tube of the type having an evacuated envelope, an axial cathode support, a magnetic system and built-in pole pieces of magnetic material disposed within said envelope, said pole pieces projecting into the space within said envelope, said holder comprising a permanent magnet having magnetic poles each of which has a pole face provided with a recess to receive and fit the external surface of an aligned pole piece of the inserted magnetron tube, said recesses being shaped to correspond to the external surfaces of the pole pieces of the inserted magnetron tube, whereby when the pole pieces of the magnetron tube are inserted in said holder, there is formed in combination with the magnets of said magnetron a unitary magnetic circuit, and a ferro-magnetic keeper associated with said magnetic circuit and means for locating the keeper in a selected terminal position with respect to the permanent magnet of the holder, wherein in one of the terminal positions of said keeper the magnetomotive force of the keeper is added to that of the magnetic system of the magnetron and the other terminal position of the keeper the magnetomotive force is removed from the magnetic system of the magnetron, thereby facilitating the withdrawal of the magnetron from the holder.

2. The combination as claimed in claim 1, including a wave guide and wherein said tube includes an output probe branch and wherein said wave guide is positioned to receive said output probe branch of the tube.

3. The combination as claimed in claim 1, wherein the external surfaces of the pole pieces of the magnetron are cylindrical and wherein the recesses in the magnetic pole pieces are arcuate to fit the surfaces of the cylindrical pole pieces of said magnetron.

4. The combination as claimed in claim 1, further including magnetic guide means leading smoothly into each of said recesses.

References Cited in the file of this patent UNITED STATES PATENTS 

